1. Field of the Invention
This invention relates to a time-setting mechanism for an analog timepiece.
2. Description of the Related Art
In order to set time by a time-setting mechanism for an analog timepiece disclosed in U.S. Pat. No. 4,636,087, at first an operation member is pulled out to move a pinion slidably mounted on the operation member so that the pinion meshes with a setting gear. When the operation member is turned in this state, the pinion is rotated therewith, and this rotation is transmitted via the setting wheel to a minute wheel. The minute gear rotates a center wheel, on which a minute hand is attached, and an hour wheel, on which an hour hand is attached, to set time.
The gears used for such conventional time-setting mechanism should have high mechanical strength because the torque of the operation member is directly applied to these gears. For this reason, these conventional gears are made of metals.
Recently, engineering plastics having high mechanical strength have been developed, and gears, made of engineering plastic materials and used in a timepiece gear train, are well known as showed in GB No. 2,127,991. Since the gears in the timepiece gear train rotate at a constant speed and with a constant torque at all time, they will not be broken even if they are made of engineering plastics as noted above. However, there is a high possibility that various gears in a time-setting mechanism are broken if these gears are made of engineering plastics like the gears in the timepiece gear train. This possibility is particularly high at the pinion and the setting wheel in the time-setting mechanism, which are brought into engagement with each other and disengaged from each other.
More specifically, when the pinion is brought into mesh with the setting wheel by pulling out an operation member at the time of the time-setting, it is highly possible that the teeth tops of the pinion and setting wheel collide with one another. If these gears are made of engineering plastic materials, the collision noted above will cause breakage or deformation of the teeth tops of the pinion and setting wheel, thus resulting in failure of transmission or failure of smooth transmission of rotation between the pinion and the setting wheel.
Further, it is liable that the teeth of the pinion are seized by the teeth of the setting wheel or conversely the teeth of the setting wheel are seized by the teeth of the pinion when the pinion is brought into mesh with the setting wheel by pulling out the operation member. When the operation member is turned in this state, its torque is concentratedly applied to the teeth of the gear that are seized by the teeth of the other gear. If the gears of the time-setting mechanism are made of engineering plastic materials, the seized teeth of the pinion or setting wheel will be broken or deformed to result in the failure of transmission or failure of smooth transmission of the rotation between the pinion and the setting wheel.
Particularly, since the setting wheel is in mesh with the minute wheel in the timepiece gear train at all time, if the teeth of the setting wheel are broken or deformed, the hands will not move normally.